An electronic personal dosimeter (EPD) is used in nuclear medicine facilities as auxiliary dosimetry devices to determine personal dose equivalent to workers working in areas where the potential for relatively high dose exists, e.g. where high therapeutic doses of radioiodine-131 and PET radionuclides are used. Their major utility is in providing real-time dose assessments of external radiation. In order to make accurate measurements, the EPD must be properly calibrated at least once per year. For routine use applications, 7 EPDs, ALOKA PDM–112 (A1, B1, B2, P4, P5, P6 and P7) were in-house calibrated to estimate personal deep dose equivalent, H_p(10), by exposing them for a certain time to a 108.07 mCi reference radioiodine-131gamma ray source (T½ 8.0207 days). This certified source was obtained from the Thailand Institute of Nuclear Technology. The EPDs were positioned with no phantom in a low background environment at 2 meters from the source and exposed to a dose and time combination, which will allow them to accumulate to the dose range from 5 to 2600 mSv. Based on the specific gamma ray constant for point source of iodine-131 in air, 2.2 mSv/h-mCi @ 1 m and an inverse square law, deviation from mean dosimeter readings of 1.9±0.87% was within the acceptable value (± 3.0%). All readings were within the permitted range (±20% of the calculated accumulative doses) with an exception for few values at doses lower than 30 mSv. The EPDs reading increases linearly as an exposure time increases. The coefficient of determination (R²) ranged from 0.902 to 1.0. In conclusion, All EPDs are well accepted to introduce into services.